Affinity - DPI can't be changed

[Vienna]

Hi!

I want to change my photos from 72 DPI to 300 DPI for printing purposes. However when I tried to change the DPI, it seemed to work in Affinity but when I checked the edited photo's DPI in Preview (I use Mac), it still shows as 72 DPI. However, when I compared and zoomed in on the original photo and the edited photo with the 300 DPI, the edited photo seems much more clearer and less pixelated than the original, and its image size in pixels became bigger as well.

The procedure I did the DPI change was: 

1. Select your image. 
2. Select Document > Resize document.
3. Change the dpi from 72 to 300 (Resample is ticked). Resample method is Bicubic. 
4. Click OK.

What can I do to be able to change the DPI to 300 for printing?

Thanks!

[Chris26]

6 hours ago, Vienna said:

I want to change my photos from 72 DPI to 300 DPI for printing purposes.

OK, i may be missing something here but if you import an image at 72 ppi and simply change the resolution to 300 ppi you will get a much smaller image but definitely print ready. I do not know what you mean by previewing it, in what may I ask?  Did you export it as a 300 ppi image after changing the resolution? In other words save it as Jpeg or PNG or something and then preview that saved image?   May I ask what you understand about changing resolutions of an image and enlarging them?

This is Photoshop, but the concepts are exactly the same in Affinity and for any software that re-sizes, don't know if this helps?

https://guides.lib.umich.edu/c.php?g=282942&p=1888163

[Richard S.]

Hi Vienna,

I obviously have no idea how much you know about resolution etc. so please excuse me if I'm advising you on matters which you already know about.

Example:

If you have a 1000px X 1000px image @ 72dpi, and then simply increase the resolution to 300 dpi - the image will shrink in size but become sharper.

HOWEVER - if you increase the dpi to 300 but still want the image to be the same dimensions (1000 x 1000) the image will pixelate badly.

With regards to resolution (dpi) - an image can always be downscaled (resulting in a sharper but smaller image) - but not upscaled, without degradation.

This is obviously a simplified answer, as there are multiple factors with regards to resolution, but I hope this helped somehow.

[John Rostron]

If you use resize to simply change the dpi from 72 to 300 without Resampling, then the pixel dimensions are unchanged but the physical dimensions will be reduced. It will not affect any pixillation when viewed at 100%.

John